Duck hepatitis is a dangerous viral disease to which ducklings are susceptible in the first 4-5 weeks of their life. If they are not protected against this disease, 40 to 50% of the young animals can perish. Therefore a protection method was sought and a vaccine suitable for immunization was developed. For the preparation of the presently used vaccine the attenuated TN virus cultivated by Asplin is used (Asplin F. D. and McLauchlan J. D.: Vet. Rec. 1954, 32, 66, 456; Asplin F. D.: Vet. Rec. 1956, 68, 412). The virus whose titer has to be at least 10.sup.4 EID.sub.50 /ml, is injected into the allantoic cavity of 10-day embryonated hen's egg in a dilution between 1:10 and 1:20; the eggs are candled daily and the eggs containing deceased embryos are taken out and destroyed in the first 24 hours. Eggs are suitable for the preparation of the vaccine in which the embryo died between 24 and 96 hours after the inoculation. The allantoamniotic fluid of the eggs (that is the fluid surrounding the embryo) is drawn off with vacuum, treated with antibiotics and filled into bottles.
The process was doubtlessly a great advance in the field of intensive large-scale poultry breeding. However the vaccine possesses disadvantages. The main disadvantage is that it is fluid and has to be stored in frozen state at a temperature of at least -20.degree. C. The substance can be stored in this state for at most half a year. In the course of transport of the frozen vaccine interruptions often occur; therefore it is preferred to transport the vaccine personally to the destination. After melting (calculated from the time of the delivery) it can be stored at a temperature of +4.degree. C. for 7 days. The vaccine is suitable for use if its titer reaches the value of 10.sup.3.5 EID.sub.50 /ml. According to our own examinations this vaccine cannot by lyophilized, although tests were carried out with numerous protective materials. The virus loss caused by the lyophilization is too high, the biological activity of the lyophilized substance is not sufficient.
At the production of this vaccine the material consumption is very high; for the preparation of 100 liters of vaccine, 23,000 embryonated hen eggs are necessary.